Lead-free piezoceramic material based on bismuth sodium titanate (BST)

ABSTRACT

The invention relates to a lead-free piezoceramic material based on bismuth sodium titanate (BST) having the following parent composition: x(Bi 0.5 Na 0.5 )TiO 3 -yBaTiO 3 -zSrTiO 3  where x+y+z=1 and 0&lt;x&lt;1, 0&lt;y&lt;1, 0≤z≤0.07 or x(Bi 0.5 Na 0.5 )TiO 3 -yBaTiO 3 -zCaTiO 3  where x+y+z=1 and 0&lt;x&lt;1, 0&lt;y&lt;1, 0&lt;z≤0.05 or x(Bi 0.5 Na 0.5 )TiO 3 -y(Bi 0.5 K 0.5 )TiO 3 -zBaTiO 3  where x+y+z=1 and 0&lt;x&lt;1, 0&lt;y&lt;1, 0≤z&lt;1, characterized by addition of a phosphorus-containing material in a quantity that gives a phosphorus concentration of from 100 to 2000 ppm in the piezoceramic material.

The invention relates to a lead-free piezoceramic material based onbismuth sodium titanate (BST) of a defined fundamental compositionaccording to the preamble of claim 1, and in particular a lead-freematerial in the meaning of the RoHS directive (guideline 2011/65/EU)having a lead content in the homogeneous material <0.1 wt. %.

Piezoactuators, piezosensors, and other piezoelectric components basedon lead zirconate titanate (PZT) represent the present prior art,wherein the requirement increasingly exists of making piezoceramicmaterials lead-free.

In a refinement of the prior art, attempts have been made to makelead-free piezoceramic materials based on BST (bismuth sodium titanate).

These materials have been known for some time and fundamentalcompositions are described in JP 62202576 (BST-BT and BST-BKT) and DE19530592 C2 (BST-BT-CT). A modification of these materials using, forexample, strontium titanate has been comprehensively described byTakenaka (Sensor and Materials; 3 (1988) 123-131).

Building on these fundamental studies, further embodiments have beendescribed in the prior art. Reference is made in this regard, forexample, to US 2002/014196 A1 and EP 1231192 A1.

A fundamental problem of all BST-based compositions is very poorcompaction during the sintering and the occurrence of so-called giantgrain growth linked to high conductivity. Piezoceramic bodies having aninhomogeneous structure may be polarized poorly, so that the desiredmaterial properties are not achieved or excessively high levels ofvariation occur in the material properties. Proposals were presented inJP 2004-075449 for suppressing giant grain growth by targetedsubstitution by manganese, chromium, iron, cobalt, or niobate.

Our own studies with respect to BST material modifications usingmanganese and copper did show partial improvements in the sinteringbehavior, but still showed an uninterrupted tendency toward giant graingrowth and worsening of electrical data.

It is thus to be stated that modified BST compositions tend toward giantgrain growth which is inhomogeneously distributed in the material ortoward the formation of a coarse-grained structure. In this case, theoccurrence of giant grains is uncontrollable and is strongly dependenton the preparation and sintering conditions. The grain growth can besuppressed by low sintering temperatures, which results in a lowsintering density of <5.6 g/cm³, however. The consequences of theundesired giant grain growth or of the coarse-grained structure are lowand strongly temperature-dependent specific electrical insulationresistance, poor polarizability of the ceramic body, and disturbedoscillation behavior of the thickness oscillation in the megahertzrange.

In our own studies, it was additionally found that the leakage currentis extremely dependent on the structure and the temperature.

Moreover, it is to be stated that modified BST compositions often have asmall sintering interval, which results in technical problems which aredifficult to control. Sintering interval is understood as the range,which is bounded by two temperature specifications, and within which therequired properties of the ceramic are achieved during the firing of thematerial. A small sintering interval therefore has the result that thedesired properties of the piezoceramic materials are only achieved ifvery small temperature tolerances can be used during the firing, whichis technologically difficult to control. A small sintering intervaltherefore results in economic disadvantages, since a relatively highproportion of the production is discards.

From the above-mentioned statements, it is the object of the inventionto specify a lead-free piezoceramic material based on BST, whichdisplays a homogeneous, fine-grained structure and has a specificelectrical insulation resistance at a temperature of 150° C. of ≥5*10⁸Ω.A further object of the invention is to specify a lead-free piezoceramicmaterial based on BST, which has a large sintering interval, inparticular a sintering interval of ≥40 K.

The object of the invention is achieved by the combination of featuresaccording to claim 1, and a method for producing a correspondingpiezoceramic material, and by a piezoceramic body or multilayer actuatorproduced on the basis of the material according to the invention.

It is accordingly based upon a lead-free piezoceramic material based onbismuth-sodium-titanate of the fundamental composition

x(Bi_(0.5)Na_(0.5))TiO₃—yBaTiO₃—zSrTiO₃ with x + y + z = 1 and 0 < x <1, 0 < y < 1, 0 ≤z ≤ 0.07 preferably 0 < x < 1, 0.1 < y < 0.25, 0 ≤ z ≤0.07 more preferably 0 < x < 1, 0.1 ≤ y ≤ 0.20, 0 ≤ z ≤ 0.03 orx(Bi_(0.5)Na_(0.5))TiO₃—yBaTiO₃—zCaTiO₃ with x + y + z = 1 and 0 < x <1, 0 < y < 1, 0 ≤ z ≤ 0.05 preferably 0 < x < 1, 0.1 < y < 0.25, 0 ≤ z ≤0.05 more preferably 0 < x < 1, 0.1 ≤ y ≤ 0.20, 0 ≤ z ≤ 0.02 orx(Bi_(0.5)Na_(0.5))TiO₃—y(Bi_(0.5)K_(0.5))TiO₃—zBaTiO₃ with x + y + z =1 and 0 < x < 1, 0 < y < 1, 0 ≤ z ≤ 1 preferably 0 < x < 1, 0.1 < y <0.3, 0 ≤ z ≤ 0.15 more preferably 0 < x < 1, 0.1 ≤ y ≤ 0.24, 0 ≤ z ≤0.05.

By adding a phosphoric material in a quantity such that theconcentration of phosphor in the piezoceramic material is 100 to 2000ppm, a piezoceramic material according to the invention is obtained.

According to the invention, the object is achieved by a lead-freepiezoceramic material based on bismuth sodium titanate (BST) of thefundamental composition

x(Bi_(0.5)Na_(0.5))TiO₃—yBaTiO₃—zSrTiO₃ with x + y + z = 1 and 0 < x <1, 0 < y < 1, 0 ≤ z ≤ 0.07 preferably 0 < x < 1, 0.1 < y < 0.25, 0 ≤ z ≤0.07 more preferably 0 < x < 1, 0.1 ≤ y ≤ 0.20, 0 ≤ z ≤ 0.03 orx(Bi_(0.5)Na_(0.5))TiO₃—yBaTiO₃—zCaTiO₃ with x + y + z = 1 and 0 < x <1, 0 < y < 1, 0 ≤ z ≤ 0.05 preferably 0 < x < 1, 0.1 < y < 0.25, 0 ≤ z ≤0.05 more preferably 0 < x < 1, 0.1 ≤ y ≤ 0.20, 0 ≤ z ≤ 0.02 orx(Bi_(0.5)Na_(0.5))TiO₃—y(Bi_(0.5)K_(0.5))TiO₃—zBaTiO₃ with x + y + z =1 and 0 < x < 1, 0 < y < 1, 0 ≤ z ≤ 1 preferably 0 < x < 1, 0.1 < y <0.3, 0 ≤ z ≤ 0.15 more preferably 0 < x < 1, 0.1 ≤ y ≤ 0.24, 0 ≤ z ≤0.05characterized by the addition of a phosphoric material in a quantitysuch that the concentration of phosphorus in the piezoceramic materialis 100 to 2000 ppm.

The specification ppm (parts per million) relates in this case to themass of phosphorus in relation to the total mass of the piezoceramiccomposition.

In one preferred embodiment, the piezoceramic material according to theinvention has a lead content of <0.1 wt. %.

In one preferred embodiment, the piezoceramic material based on bismuthsodium titanate (BST) according to the invention is embodied so that ithas the fundamental composition

x(Bi_(0.5)Na_(0.5))TiO₃—yBaTiO₃—zSrTiO₃ with y ≥ 0.1 and x + y + z = 1or x(Bi_(0.5)Na_(0.5))TiO₃—yBaTiO₃—zCaTiO₃ with y ≥ 0.1 and x + y + z =1 or x(Bi_(0.5)Na_(0.5))TiO₃—y(Bi_(0.5)K_(0.5))TiO₃—zBaTiO₃ with y ≥ 0.1and x + y + z = 1,wherein an addition of a phosphoric material is performed in a quantitysuch that the concentration of phosphorus in the piezoceramic materialis 100 to 2000 ppm.

In one preferred embodiment, the lead-free piezoceramic material isembodied so that the phosphoric compound is an inorganic phosphate,hydrogen phosphate, or dihydrogen phosphate.

In a particularly preferred embodiment, the lead-free piezoceramicmaterial is embodied so that the phosphoric compound is selected fromthe group which consists of KH₂PO₄ (KDP) and (NH₄)H₂PO₄ (ADP).

While the effect according to the invention of the addition of thephosphoric material is achieved in a broad quantity range, it has beenshown that particularly advantageous properties are achieved if thelead-free piezoceramic material is embodied so that the phosphoricmaterial is added in a quantity such that the concentration ofphosphorus in the lead-free piezoceramic material is 100 to 2000 ppm.

It has been shown that if the concentration of phosphorus in the ceramicmaterial according to the invention exceeds 2000 ppm, the ability toprocess the material mixture to form the piezoceramic material worsens.At concentrations of less than 100 ppm, the effect sought according tothe invention is no longer achieved to a sufficient extent.

In one preferred embodiment, the phosphoric material is used in aquantity such that the concentration of phosphorus in the lead-freepiezoceramic material is 250 to 2000 ppm, more preferably 270 to 1800ppm.

It has been shown that the properties of the lead-free piezoceramicmaterial can be influenced in a particularly advantageous manner in thatthe fundamental composition contains additives in the form of oxides orcomplex perovskites.

It is surprisingly possible using the lead-free piezoceramic materialaccording to the invention to set the sintering interval to ≥40 K.

The invention also relates to a method for producing the variouslead-free piezoceramic materials. The method according to the inventionis preferably embodied so that it comprises the following steps:

-   -   producing a raw material mixture of the fundamental composition,    -   producing a calcinate of the fundamental composition,    -   finely grinding the calcinate,    -   producing a granulate in particular by spray granulation or        producing a casting slurry for the multilayer or “co-firing”        process,    -   further processing in a known manner including sintering in        normal atmosphere.

A “cofiring” process is to be understood in the meaning of the presentinvention as a particularly innovative production method, in which filmsmade of piezoceramic material are firstly cast and subsequently areprovided with electrodes while still in the green state. A piezoelementis laminated from many individual films and subsequently sinteredjointly with the internal electrodes in a single processing step, asdescribed, for example, in DE 10234787.

The addition of phosphorus or phosphoric materials can be performedduring the fine grinding and/or the preparation of a spray slurry orcasting slurry.

The method according to the invention is particularly preferablyembodied so that the addition of phosphorus or phosphoric materialstakes place during the preparation of the spray slurry or castingslurry. This method has the advantage that firstly a large-scaleindustrial production of a finely-ground powder of the fundamentalcomposition takes place and the quantity and type of the phosphorusaddition can be adapted to the requirements of the subsequent processingsteps (spray slurry, casting slurry).

In one particularly preferred method for producing the lead-freepiezoceramic material according to the invention, a calcinate of thefundamental composition is firstly provided. An addition of phosphorusis then performed, preferably in the form of KDP or ADP, which areferroelectric as a single crystal, in a concentration of 270 to 1800ppm. The addition can be performed during the fine grinding or duringthe preparation of the spray slurry or casting slurry. The furtherprocessing of the material of this type, including sintering in normalatmosphere, is performed according to known technologies.

In addition, a piezoceramic multilayer actuator based on theabove-described piezoceramic material is according to the invention.Such a piezoceramic multilayer actuator is known, for example, from DE10234787 or DE 20 2012012009.

The invention also relates to a piezoelectric component based on theabove-described piezoceramic material, which consists of at least onepiezoceramic body having at least two electrodes, and in particular alsoto a piezoelectric ultrasonic transducer, which is operated inparticular in its thickness oscillation.

The phosphoric material used can be understood as a sintering aid,wherein the phosphorus component is decisively important here. Theprejudice of the technical world, according to which phosphorus—althoughit does inhibit the grain growth in a positive manner—worsens thepiezoelectric properties of corresponding piezoceramic materials, isovercome by the targeted addition of phosphorus to the BST fundamentalcomposition.

Surprisingly, it has been shown that by the use of the phosphoricmaterial, not only can effective suppression of the giant grain growthand therefore a homogeneous, fine-grained structure be achieved, butrather a broad sintering interval of ≥40 K the piezoceramic material isalso achieved at the same time. This is of great significancetechnologically, because a broad sintering interval is a prerequisitefor cost-effective production of the material, multilayer actuator, orcomponent. In addition, the piezoceramic materials according to theinvention have a high specific electrical insulation resistance of≥5*10⁸Ω, which is very advantageous for the use in the describedcomponents.

With the piezoceramic material according to the invention, ahomogeneous, fine-grained structure results in a broad sinteringinterval of ≥40 K, in the temperature range from 1120° C. to 1240° C. Inaddition, an increase of the insulation resistance at high temperaturesand therefore better polarization behavior are to be noted asadvantages. An actuator produced on the basis of the lead-freepiezoceramic material according to the invention has a high insulationresistance over a broad temperature range, while an ultrasonictransducer according to the invention has pronounced thicknessoscillation with high coupling factor.

It remains to be noted that surprisingly the use of phosphoric additivesresults in an inhibition of the giant grain growth and a homogeneous,fine-grained structure, and the location of the depolarizationtemperature can be influenced within certain limits by the type andquantity of the phosphorus addition.

Phosphoric additives can be added during the fine grinding or the spraygranulation. However, the use of phosphoric dispersing agents and/oradditives during the preparation of casting slurries or the use ofphosphoric binders during the preparation of such slurries is alsoconceivable.

With suitable selection of the phosphoric dispersing agents and/oradditives, the technical advantage results that the viscosity of finelyground, casting, or spray slurry is not negatively influenced.

In addition, a phosphorus introduction can be used which issubstantially greater than the value introduced by typical raw materialcontamination and typical dispersing agent concentrations and in thecase of which the added phosphorus quantity can be set in a targetedmanner.

One possible alternative is the phosphorus addition during the rawmaterial mixing or an infiltration of solids using phosphoric liquids.However, it is also conceivable to incorporate phosphorus as an acceptordopant in the fundamental composition (partial replacement of titaniumby phosphorus).

It has been shown that the addition of the phosphorus to the materialaccording to the invention can be performed in the form of nearly anyarbitrary phosphoric material. Although potassium dihydrogen phosphateor ammonium dihydrogen phosphate are particularly preferred phosphoricmaterials, the addition of phosphorus can also be performed by arbitraryother phosphoric materials.

The inventors of the present application have established by theirstudies that a certain reduction of the depolarization temperatureaccompanies the addition of the phosphoric material. The effect of thereduction of the depolarization temperature is different in this casefor different phosphoric materials. It has thus been shown that, forexample, if ammonium dihydrogen phosphate is added, a substantiallystronger drop of the depolarization temperature occurs than upon theaddition of potassium dihydrogen phosphate. This unexpected effect hasthe result that the present invention has the further advantage that thereduction of the depolarization temperature can be controlled withincertain limits by the selection of the additional phosphoric material,with otherwise uniform properties of the piezoceramic material. This issignificant because a specific depolarization temperature is sought independence on the desired intended use of the piezoceramic material.While it generally appears desirable to seek the smallest possiblereduction of the depolarization temperature, it can be entirely usefulfor specific applications to achieve a stronger reduction of thedepolarization temperature. This applies in particular for intended usesin which the piezoceramic materials only have to be functional in a verynarrow temperature interval. For such applications, it can be entirelyreasonable to seek a stronger reduction of the depolarizationtemperature, since the desirable piezoelectric properties of thepiezoceramic materials improve upon the approach to the depolarizationtemperature from below.

The invention additionally also relates to the use of a phosphoricmaterial in a piezoceramic material based on bismuth sodium titanate(BST) of the above-mentioned fundamental composition to reduce the giantgrain growth and to achieve a homogeneous, fine-grained structure,wherein the phosphoric material is used in a quantity such that theconcentration of phosphorus in the piezoceramic material is 100 to 2000ppm, in particular 250 to 2000 ppm, more preferably 270 to 1800 ppm. Theinvention will be explained in greater detail hereafter on the basis ofan exemplary embodiment and the description of comparative experiments.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS(S)

FIG. 1 is a flow chart illustrating one embodiment of the method forproducing a lead-free piezoceramic material of the present invention.

FIGS. 2 and 3 are a graph showing the curve of the sintering density forthe fundamental composition 0.85(Bi_(0.5)Na_(0.5))TiO₃ -0.12BaTiO₃ -0.03SrTiO₃ in dependence on the sintering temperature and thecorresponding light microscopy structure recordings, respectively.

FIG. 4 is a graph illustrating the extreme drop of the insulationresistance with the sample temperature.

FIGS. 5a and 5b are graphs showing the electrical conductivity versuselectrical field strength of samples at various temperatures.

FIG. 6 are graphs which depict the curve of impedance and phase of thethickness oscillation for the samples sintered at differenttemperatures.

FIG. 7 is a series of light microscopy structure recordings of samples 2a to 2 h.

FIG. 8 is a graph showing the curve of the sintering density independence on the sintering temperature of samples 2 a to 2 c, 2 e and 2g.

FIG. 9 is a graph showing the substantial increase of the specificinsulation resistance of samples 2 a to 2 h at higher temperatures.

FIGS. 10a-10e are graphs showing the electrical conductivity versuselectrical field strength of samples containing various concentrationsof phosphorous at various temperatures.

FIG. 11 are graphs which depict the characteristic resonance curves ofthe samples sintered at different temperatures.

FIG. 12 is a graph showing the depolarization temperature Td fordifferent phosphorus sources and proportions.

FIGS. 13 and 14 are graphs showing the electromechanical elongation andthe sample current in the temperature range from 25 to 150° C. for acomposition according to the present invention.

EXAMPLES

The measurement results set forth hereafter relate to the fundamentalsystem x(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zSrTiO₃.

FIG. 1 describes the general technological sequence of the sampleproduction. The technological steps in which the addition of phosphoricmaterials as described in the claims can be performed are identifiedwith “*”.

The mixing of the raw materials and the fine grinding of the calcinatewere each performed in an agitator bead mill.

Phosphoric additions were performed specifically during the followingtechnological steps:

FM fine grinding G addition during the granulation VS addition duringthe organic slurrying for the film production

The structure characterization was performed according to the followingclassification:

0 material not processable 1 fine-grained, homogeneous structure 2inhomogeneous structure, giant grain growth 3 coarse-grained structure

The sample density was determined on sintered cylinders according to thebuoyancy method and is specified either as a mean value for thespecified sintering temperature or as the “density in g/cm³>” for thelowest sintering temperature having measurable electrical values in thespecified temperature range.

For the electrical measurements, metallized samples having a diameter of12 mm, an insulation edge of 0.5 mm, and a thickness of 0.5 mm wereused. The polarization was performed at 80° C., 15 minutes, 5 kV/mm.

Samples having strong variation of the measured values, disturbance ofthe resonance curves, or excessively low maximum phase angle in theradial or thickness oscillation are identified by “S”.

The coupling factors of the radio and thickness oscillation are k_(p)and k_(t), respectively.

The depolarization temperature T_(d) is generally defined as theinflection point in the temperature dependence of the dielectricconstant of polarized samples.

The specific insulation resistance ρ_(is) is determined at 50 V onpolarized samples with temperature increase from room temperature up to200° C.

The electromechanical elongation S₃ is determined by means of laserinterferometer at 2 kV/mm. The value at room temperature and theassociated sample current I are specified in the table.

Characteristic values in the studied temperature range are shown inTable 2.

The diagrams and light microscopy structure recordings relate to thecomposition defined in the table under the respective sample number.

The prior art and the deficiencies to be remedied are to be described ingreater detail hereafter:

TABLE 1 sintering No. x y z ρ in ppm temperature ° C. Density in g/cm³Structure S ε 1a 0.850 0.120 0.030 0 1120 5.2 1 460 1b 0.850 0.120 0.0300 1140 5.5 1 S 570 1c 0.850 0.120 0.030 0 1160 5.6 1 530 1d 0.850 0.1200.030 0 1180 5.7 2 590 1e 0.850 0.120 0.030 0 1200 5.7 3 S 480 1f 0.8500.120 0.030 0 1220 5.7 3 S 480 ρ_(is) in Ωm ρ_(is) in Ωm RT, 2 kV/mm No.tanδ × 10³ kp kt Td in ° C. (RT) (150° C.) S3 × 10³ I in A 1a 16 0.120.37 215 6.1E+08 8.0E+05 0.25 6.9E−07 1b 119 0.10 0.21 210 2.0E+081.0E+06 0.19 3.2E−06 1c 13 0.12 0.40 210 1.1E+10 1.8E+06 0.23 3.8E−07 1d16 0.13 0.41 210 1.8E+10 4.0E+06 0.27 4.1E−07 1e 44 0 0 220 1.9E+093.6E+06 0.31 5.5E−07 1f 79 0 0 230 9.1E+08 1.9E+06 0.32 3.1E−07

FIG. 2, samples 1 a to 1 f from Table 1, shows the curve of thesintering density for the fundamental composition0.85(Bi_(0.5)Na_(0.5))TiO₃-0.12BaTiO₃-0.03SrTiO₃ in dependence on thesintering temperature. The low density at low sintering temperatures,the narrow sintering interval, and the drop of the density at highsintering temperatures caused by the decomposition of the samples(vaporization Bi, Na) are characteristic.

The corresponding light microscopy structure recordings (FIG. 3) showthe transition from the fine-grained, insufficiently compacted materialto the giant grain growth in the middle of the studied temperature rangeand to coarse-grained structure at higher sintering temperatures.

The extreme drop of the insulation resistance with the sampletemperature has proven to be disadvantageous (FIG. 4, samples 1 a to 1f). The results are insufficient or undefined polarization andexcessively low or strongly varying electrical values.

The non-tolerable electrical conductivity is clearly recognizable in thedepiction of the sample current at higher electrical field strengths andhigher temperatures (FIG. 5a , samples 1 a to 1 f, 5 b, sample 1 d). Theoperating temperature of actuators is thus significantly restricted.

The depiction of the curve of impedance and phase of the thicknessoscillation for the samples sintered at different temperatures (FIG. 6,samples 1 a to 1 f) discloses a relationship between structure andresonance behavior (3 individual samples are shown in each case). Thematerial is characterized by

-   -   strong variation of the curve profiles at the respective        sintering temperature,    -   strong variation of the curve profiles upon variation of the        sintering temperature, and    -   extremely disturbed resonance behavior at higher sintering        temperatures.

The data are summarized in Table 1.

It is therefore shown that none of the applied sintering temperaturesresults in sufficiently good and reproducible electrical orelectromechanical values and the previous technology is not suitable forlarge-scale industrial production.

Comparable behavior is shown by samples 2 a, 5 a, 9 a, 10 a, 14, and 15,which are listed in Table 2 but do not fall in the scope of the claims.

TABLE 2 sintering ρ_(is) in Ωm ρ_(is) in Ωm RT, 2 kV/mm No. x y z Paddition addition at ρ in ppm temperature ° C. Density in g/cm³Structure S ε tanδ × 10³ kp kt Td in °C (RT) (150° C.) S3 × 10³ I in A 2a 0.850 0.120 0.030 0 1160-1240 5.6 2 S 550 12 0 0 195 1.9E+10 5.7E+060.32 3.7E−07  5a 0.850 0.120 0.030 0 1180-1220 5.6 2 540 9 0.12 0.46 2051.5E+11 9.5E+06 0.30 3.7E−07  9a 0.770 0.200 0.030 0 1180-1220 5.6 1 50021 0.17 0.41 215 3.8E+10 1.1E+09 0.26 3.0E−07 10a 0.970 0.030 0.000 01120-1180 5.7 2 S 360 11 0.20 0.40 195 2.3E+10 3.6E+06 0.18 3.0E−07 140.850 0.150 0.000 0 1160-1220 5.5 1 530 19 0.14 0.40 235 9.9E+10 1.6E+080.26 3.0E−07 15 0.850 0.150 0.000 0 1160-1220 5.6 3 440 9 0.11 0.46 2351.3E+11 1.3E+07 0.25 2.0E−07  2b 0.850 0.120 0.030 PE169 FM 2501160-1240 5.7 1 750 27 0.16 0.42 180 3.8E+10 3.8E+09 0.34 5.0E−07  40.850 0.120 0.030 PE169 FM 250 1160-1220 5.6 1 670 22 0.16 0.42 2005.7E+10 19.E+09 0.34 4.4E−07  6 0.850 0.120 0.030 PE169 FM 500 1180-12205.6 1 780 25 0.16 0.42 185 1.1E+11 7.6E+09 0.35 4.9E−07  7 0.850 0.1200.030 PE169 FM 250 1180-1220 5.7 1 640 24 0.16 0.40 200 5.7E+10 3.8E+090.30 3.7E−07  8 0.790 0.180 0.030 PE169 FM 250 1180-1220 5.7 1 550 240.16 0.40 205 9.5E+10 9.5E+09 0.25 3.0E−07  9b 0.770 0.200 0.030 PE169FM 250 1180-1220 5.6 1 560 23 0.16 0.40 205 3.8E+10 3.8E+09 0.25 3.0E−0714a 0.850 0.150 0.000 PE169 FM 250 1160-1220 5.7 1 630 24 0.16 0.43 2101.4E+11 5.5E+09 0.30 4.0E−07  2c 0.850 0.120 0.030 KDP G 115 1180-12203.7 2 600 37 0.16 0.35 205 3.8E+09 9.5E+06 0.32 4.4E−07  2d 0.850 0.1200.030 KDP G 225 1180-1220 5.7 2 700 25 0.16 0.41 200 1.5E+10 5.7E+070.32 4.4E−07  2e 0.850 0.120 0.030 KDP G 285 1180-1220 5.7 1 710 26 0.160.41 200 1.1E+11 3.8E+09 0.32 4.4E−07  2f 0.850 0.120 0.030 KDP G 5701180-1220 5.7 1 740 28 0.16 0.41 195 1.1E+11 1.9E+09 0.31 4.8E−07  2g0.850 0.120 0.030 KDP G 1140 1180-1220 5.7 1 770 26 0.15 0.39 1901.1E+11 3.8E+09 0.30 5.2E−07  2h 0.850 0.120 0.030 KDP G 1705 1180-12205.7 1 780 27 0.15 0.37 185 7.6E+10 4.7E+09 0.30 5.2E−07  2i 0.850 0.1200.030 KDP G 2275 1180-1220 0  3 0.850 0.120 0.030 KDP G 285 1160-12205.6 1 720 27 0.16 0.41 195 8.5E+10 6.5E+09 0.34 4.9E−07  5b 0.850 0.1200.030 KDP G 455 1160-1220 5.7 1 770 28 0.16 0.41 195 3.8E+10 1.7E+090.35 5.4E−07 10b 0.970 0.030 0.000 KDP G 115 1120-1180 5.8 2 S 330 110.19 0.40 195 1.4E+10 2.3E+06 0.19 3.0E−07 10c 0.970 0.030 0.000 KDP G1140 1120-1180 5.8 1 440 37 0.18 0.35 185 7.2E+10 1.2E+09 0.20 6.0E−0710d 0.970 0.030 0.000 KDP G 1705 1120-1180 5.8 1 460 40 0.16 0.31 1805.7E+10 5.7E+08 0.18 7.0E−07 11 0.900 0.100 0.000 KDP G 285 1160-12205.7 1 740 32 0.15 0.41 195 1.6E+10 4.4E+09 0.35 5.3E−07 12 0.880 0.1200.000 KDP G 285 1160-1220 5.7 1 690 25 0.16 0.42 210 1.3E+10 3.4E+090.32 5.2E−07 13 0.860 0.140 0.000 KBP G 285 1160-1220 5.7 1 630 24 0.160.41 225 3.0E+10 7.0E+08 0.30 5.1E−07 15a 0.850 0.150 0.000 KDP G 2851160-1220 5.7 1 610 23 0.16 0.42 230 7.2E+10 5.7E+09 0.30 3.0E−07  2j0.850 0.120 0.030 ADP G 135 1180-1220 5.7 2 690 35 0.16 0.41 200 7.6E+103.8E+09 0.35 4.2E−07  2k 0.850 0.120 0.030 ADP G 675 1180-1220 5.8 1 82025 0.16 0.41 175 7.6E+10 3.8E+09 0.35 5.4E−07  2l 0.850 0.120 0.030 ADPG 1345 1180-1220 5.8 1 940 31 0.16 0.37 150 3.8E+10 5.7E+09 0.35 6.2E−07 2m 0.850 0.120 0.030 ADP G 2695 1180-1220 0  2n 0.850 0.120 0.030 PE169VS 570 1160-1220 5.7 1 730 25 0.16 0.44 185 1.3E+11 3.0E+09 0.36 4.7E−07

The following exemplary embodiments show the behavior of compositionsproduced according to the invention.

Exemplary Embodiment 1:

The fundamental composition0.85(Bi_(0.5)Na_(0.5))TiO₃-0.12BaTiO₃-0.03SrTiO₃ was processed accordingto the flow chart (FIG. 1) and

-   -   either a phosphoric dispersing agent was added during the fine        grinding (PE169, producer Akzo Nobel)    -   or potassium dihydrogen phosphate was introduced during the        granulation by addition to the binder.

Samples 2 i with 2275 ppm P (TP) and 2 m with 2695 ppm P (ADP) were notprocessable in this manner.

As may be seen from the light microscopy structure recordings (FIG. 7,samples 2 a to 2 h), an addition according to the invention ofphosphorus ≥250 ppm causes the creation of a homogeneous, fine-grainedstructure.

FIG. 8 (samples 2 a, 2 b, 2 c, 2 e, and 2 g) shows a significantimprovement of the compaction upon addition of quantities according tothe invention of phosphorus ≥250 ppm.

In addition, a substantial increase of the specific insulationresistance is surprisingly shown at higher temperatures, by multipleorders of magnitude (FIG. 9, samples 2 a to 2 h). Sufficiently good,reproducible polarization of the samples is thus ensured from 250 ppm.

FIGS. 10a to 10e make it clear that with phosphorus proportionsaccording to the invention ≥250 ppm, a substantial reduction of thesample current is to be noted even at higher temperatures. The operationof actuators is thus also possible at higher operating temperatures.

The variation of the sample properties is substantially reduced. If oneobserves characteristic resonance curves of the samples sintered atdifferent temperatures it is thus noticeable that with phosphorusproportions according to the invention ≥250 ppm, the differences betweenthe samples sintered at different temperatures are substantially reducedand therefore the sintering interval may surprisingly be broadened to atechnologically usable, easily implementable temperature range (Tables3a, 3b, FIG. 11).

TABLE 3a Sample 2b ε tanδ × 10³ kp kt ρ_(is) in Ωm (RT) ρ_(is) in Ωm(150° C.) S3 × 10³ I in A 1160 750 29 0.16 0.40 2.0E+10 3.4E+09 0.366.3E−07 1180 730 27 0.17 0.42 3.8E+10 3.8E+09 0.34 5.0E−07 1200 750 270.17 0.41 2.0E+10 3.4E+09 0.34 5.4E−07 1220 770 27 0.16 0.42 2.6E+103.7E+09 0.32 5.9E−07 1240 730 27 0.16 0.42 2.0E+10 3.4E+09 0.32 5.9E−07

TABLE 3b Sample 2e ε tanδ × 10³ kp kt ρ_(is) in Ωm (RT) ρ_(is) in Ωm(150° C.) S3 × 10³ I in A 1180 710 27 0.16 0.43 1.7E+11 5.1E+09 0.324.4E−07 1200 710 26 0.16 0.41 3.4E+10 1.3E+09 0.33 4.8E−07 1220 700 250.17 0.42 1.1E+11 3.8E+09 0.34 4.6E−07

Surprisingly, the depolarization temperature may be set in a broad rangeby selection of the phosphoric material. FIG. 12 (samples 2 a, 2 c to 2h, 2 j to 2 l) displays the depolarization temperature Td, for differentphosphorus sources and proportions. The possibility is therefore openedup of varying the depolarization temperature specifically for theapplication.

Exemplary Embodiment 2:

Samples 3, 4, 5 b, 6, and 2 n according to Table 2 are further examplesof the modification according to the invention, which is applicable inlarge-scale industrial processes, of the fundamental composition0.85(Bi_(0.5)Na_(0.5))TiO₃-0.12BaTiO₃-0.03SrTiO₃.

It can be seen as an essential technological advantage that in examples3 and 5b, the material was processed without phosphorus up to the finegrinding and the phosphorus was first added during the slurrying for thespray granulation.

In examples 4, 6, the phosphorus addition was performed during the finegrinding, in example 2n during the organic slurrying for the filmcasting.

It is advantageous that the large-scale industrial material processingis performed uniformly up to the fine grinding independently of theprimary shaping process (compression or film casting) and therefore thetype and quantity of the phosphorus addition can be optimally adapted tothe respective shaping process.

However, the possible combination of viscosity-determining phosphoricdispersing agents or binders and substantially “viscosity-neutral”additives such as KDP or ADP can also be advantageous.

FIGS. 13 and 14, sample 3, show the electromechanical elongation and thesample current in the temperature range from 25 to 150° C. for acomposition according to the invention.

Exemplary Embodiment 3:

No. x y z P addition addition at ρ in ppm  7 0.850 0.120 0.030 PE169 FM250  8 0.790 0.180 0.030 PE169 FM 250  9a 0.770 0.200 0.030 0  9b 0.7700.200 0.030 PE169 FM 250 10a 0.970 0.030 0.000 0 10b 0.9.70 0.030 0.000KDP G 115 10c 0.970 0.030 0.000 KDP G 1140 10d 0.970 0.030 0.000 KDP G1705 11 0.900 0.100 0.000 KDP G 285 12 0.880 0.120 0.000 KDP G 285 130.860 0.140 0.000 KDP G 285 14 0.850 0.150 0.000 0 14a 0.850 0.150 0.000PE169 FM 250 15 0.850 0.150 0.000 15a 0.850 0.150 0.000 KDP G 285

Excerpt from Table 2

In the range y≥0.10, the material system behaves similarly with respectto the phosphorus modification as the fundamental composition0.85(Bi_(0.5)Na_(0.5))TiO₃-0.12BaTiO₃-0.03SrTiO₃.

The range y<0.10 requires phosphorus proportions in the upper claimedvalue range.

The invention claimed is:
 1. A lead-free piezoceramic material based onbismuth sodium titanate (BST) of the fundamental compositionx(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zSrTiO₃ with x+y+z=1 and 0<x<1, 0<y<1,0≤z≤0.07 or x(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zCaTiO₃ with x+y+z=1 and0<x<1, 0<y<1, 0≤z≤0.05 characterized by the addition of a phosphoricmaterial in a quantity such that the concentration of phosphorus in thepiezoceramic material is 250 to 2000 ppm, wherein the specification ppm(parts per million) relates to the mass of phosphorus in relation to thetotal mass of the piezoceramic composition.
 2. The lead-freepiezoceramic material based on bismuth sodium titanate (BST) accordingto claim 1, wherein the fundamental composition isx(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zSrTiO₃ with y≥0.1 and x+y+z=1 orx(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zCaTiO₃ with y≥0.1 and x+y+z=1.
 3. Thelead-free piezoceramic material according to claim 1, in that thephosphoric compound is an inorganic phosphate, hydrogen phosphate, ordihydrogen phosphate.
 4. The lead-free piezoceramic material accordingto claim 1, characterized in that the phosphoric compound is selectedfrom the group which consists of KH₂PO₄, (NH₄)H₂PO₄.
 5. The lead-freepiezoceramic material according to claim 1, characterized in that thephosphoric material is added in a quantity such that the concentrationof phosphorus in the lead-free piezoceramic material is 270 to 1800 ppm.6. The lead-free piezoceramic material according to claim 1,characterized in that the fundamental composition contains additives inthe form of oxides or complex perovskites.
 7. A method for producing alead-free piezoceramic material according to claim 1, characterized bythe following steps: producing a raw material mixture of the fundamentalcomposition, producing a calcinate of the fundamental composition,finely grinding the calcinate, producing a granulate in particular byspray granulation or producing a casting slurry for the multilayer or“co-firing” process, further processing in a known manner includingsintering in normal atmosphere, wherein phosphoric additives are addedduring the fine grinding or the spray granulation and/or during thepreparation of casting slurries.
 8. A piezoceramic multilayer actuatorbased on a lead-free piezoceramic material according to claim
 1. 9. Apiezoceramic component, preferably having at least one piezoceramic bodyhaving at least two electrodes, more preferably in the form of apiezoelectric ultrasonic transducer, based on a lead-free piezoceramicmaterial according to claim
 1. 10. A use of a phosphoric material in apiezoceramic material based on bismuth sodium titanate (BST) of thefundamental composition x(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zSrTiO₃ withx+y+z=1 and 0<x<1, 0<y<1, 0≤z≤0.07 orx(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zCaTiO₃ with x+y+z=1 and 0<x<1, 0<y<1,0≤z≤0.05 to reduce the giant grain growth, wherein the phosphoricmaterial is used in a quantity such that the concentration of phosphorusin the piezoceramic material is 250 to 2000 ppm, wherein thespecification ppm (parts per million) relates to the mass of phosphorusin relation to the total mass of the piezoceramic composition.
 11. Theuse according to claim 10, wherein the fundamental composition isx(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zSrTiO₃ with y≥0.1 and x+y+z=1 orx(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zCaTiO₃ with y≥0.1 and x+y+z=1.
 12. Theuse according to claim 10, characterized in that the phosphoric compoundis an inorganic phosphate, hydrogen phosphate, or dihydrogen phosphate.13. The use according to claim 10, characterized in that the phosphoriccompound is selected from the group which consists of KH₂PO₄,(NH₄)H₂PO₄.
 14. A use of a phosphoric material in a piezoceramicmaterial based on bismuth sodium titanate (BST) of the fundamentalcomposition x(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zSrTiO₃ with x+y+z=1 and0<x<1, 0<y<1, 0<z<0.07 or x(Bi_(0.5)Na_(0.5))TiO₃-yBaTiO₃-zCaTiO₃ withx+y+z=1 and 0<x<1, 0<y<1, 0<z<0.05 to reduce the giant grain growth,wherein the phosphoric material is used in a quantity such that theconcentration of phosphorus in the piezoceramic material is 270 to 1800ppm, wherein the specification ppm (parts per million) relates to themass of phosphorus in relation to the total mass of the piezoceramiccomposition.